Conventional spark plugs are designed for providing a spark to ignite a gas in a cylinder of an engine. The gas is a fuel-air mixture, the fuel coming from a gasoline tank, and the air coming from a spacing washer intermediate between the casing thread of the spark plug screwed into the cylinder head of the engine, and through a very small aperture formed between the closely screwed threads of the plug casing, through the engine cylinder, and into the engine. The entry of air by the way described above makes possible blockage of the air ventilation when some dust attaches in the aperture. Such a blockage of air ventilation results in a lack of air assistant to the engine which reduces the degree of combustion to a very low level. Another known type of spark plug, has an air chamber formed between a medium body part of the plug and an outer surounding iron sheath wich is ventilated with lattice openings, inside of which a mesh put around the chamber operates as an air filling device. Some and small hollows are bored through the bottom of the chamber to the casing thread (which thread is for screwing the plug into cylinder head of an engine). Air therefore can pass through the ventilated iron sheath and through the mesh (for filtering purposes) to the air chamber and then converts to flow through the bottom hollows to the aperture of the screwed together threads (when the plug is already screwed into the engine in order) to the cylinder of the engine to mix with the fuel. The entry of the air by this route may keep out dust which blocks the aperture of the screwed threads, but the aperture is nevertheless very small and whenever some carbon pearls are produced in engine they might block the passage of the air and cause combustion to deteriorate.